Underline URLs on mouse hover

Track hovered URL span in the messages component and apply underline
styling during rendering. Switch mouse mode from CellMotion to
AllMotion so hover events fire without a button held.

Assisted-By: docker-agent

Author: dgageot

pkg/tui/components/messages/lineutil.go

@@ -0,0 +1,26 @@
+package messages
+
+import (
+	"charm.land/lipgloss/v2"
+	"github.com/charmbracelet/x/ansi"
+	"github.com/mattn/go-runewidth"
+)
+
+// styleLineSegment applies a lipgloss style to the portion of a line between
+// startCol and endCol (display columns), preserving the text before and after.
+// ANSI codes in the styled segment are stripped so the style renders cleanly.
+func styleLineSegment(line string, startCol, endCol int, style lipgloss.Style) string {
+	plainLine := ansi.Strip(line)
+	plainWidth := runewidth.StringWidth(plainLine)
+
+	if startCol >= plainWidth || startCol >= endCol {
+		return line
+	}
+	endCol = min(endCol, plainWidth)
+
+	before := ansi.Cut(line, 0, startCol)
+	segment := ansi.Strip(ansi.Cut(line, startCol, endCol))
+	after := ansi.Cut(line, endCol, plainWidth)
+
+	return before + style.Render(segment) + after
+}

pkg/tui/components/messages/messages.go

@@ -130,6 +130,9 @@ type model struct {
 
 	// Hover state for showing copy button on assistant messages
 	hoveredMessageIndex int // Index of message under mouse (-1 = none)
+
+	// Hovered URL for underline-on-hover effect (nil = no URL hovered)
+	hoveredURL *hoveredURL
 }
 
 // New creates a new message list component
@@ -365,7 +368,7 @@ func (m *model) handleMouseMotion(msg tea.MouseMotionMsg) (layout.Model, tea.Cmd
 	}
 
 	// Track hovered message for showing copy button on assistant messages
-	line, _ := m.mouseToLineCol(msg.X, msg.Y)
+	line, col := m.mouseToLineCol(msg.X, msg.Y)
 	newHovered := -1
 	if msgIdx, _ := m.globalLineToMessageLine(line); msgIdx >= 0 && msgIdx < len(m.messages) {
 		if m.messages[msgIdx].Type == types.MessageTypeAssistant {
@@ -384,6 +387,9 @@ func (m *model) handleMouseMotion(msg tea.MouseMotionMsg) (layout.Model, tea.Cmd
 		m.renderDirty = true
 	}
 
+	// Track hovered URL for underline effect
+	m.updateHoveredURL(line, col)
+
 	return m, nil
 }
 
@@ -566,6 +572,8 @@ func (m *model) View() string {
 		visibleLines = m.applySelectionHighlight(visibleLines, startLine)
 	}
 
+	visibleLines = m.applyURLUnderline(visibleLines, startLine)
+
 	// Sync scroll state and delegate rendering to scrollview which guarantees
 	// fixed-width padding, pinned scrollbar, and exact height.
 	m.scrollview.SetContent(m.renderedLines, m.totalScrollableHeight())
@@ -1239,6 +1247,7 @@ func (m *model) LoadFromSession(sess *session.Session) tea.Cmd {
 	m.bottomSlack = 0
 	m.selectedMessageIndex = -1
 	m.hoveredMessageIndex = -1
+	m.hoveredURL = nil
 
 	var cmds []tea.Cmd
 

pkg/tui/components/messages/selection.go

@@ -255,24 +255,7 @@ func (m *model) applySelectionHighlight(lines []string, viewportStartLine int) [
 
 // highlightLine applies selection highlighting to a portion of a line
 func (m *model) highlightLine(line string, startCol, endCol int) string {
-	// Get plain text for boundary checks
-	plainLine := ansi.Strip(line)
-	plainWidth := runewidth.StringWidth(plainLine)
-
-	// Validate and normalize boundaries
-	if startCol >= plainWidth || startCol >= endCol {
-		return line
-	}
-	endCol = min(endCol, plainWidth)
-
-	// Extract the three parts while preserving ANSI codes
-	before := ansi.Cut(line, 0, startCol)
-	selectedText := ansi.Cut(line, startCol, endCol)
-	selectedPlain := ansi.Strip(selectedText)
-	selected := styles.SelectionStyle.Render(selectedPlain)
-	after := ansi.Cut(line, endCol, plainWidth)
-
-	return before + selected + after
+	return styleLineSegment(line, startCol, endCol, styles.SelectionStyle)
 }
 
 // clearSelection resets the selection state

pkg/tui/components/messages/urldetect.go

@@ -3,10 +3,20 @@ package messages
 import (
 	"strings"
 
+	"charm.land/lipgloss/v2"
 	"github.com/charmbracelet/x/ansi"
 	"github.com/mattn/go-runewidth"
 )
 
+var underlineStyle = lipgloss.NewStyle().Underline(true)
+
+// hoveredURL tracks the URL currently under the mouse cursor.
+type hoveredURL struct {
+	line     int // global rendered line
+	startCol int // display column where URL starts
+	endCol   int // display column where URL ends (exclusive)
+}
+
 // urlAtPosition extracts a URL from the rendered line at the given display column.
 // Returns the URL string if found, or empty string if the click position is not on a URL.
 func urlAtPosition(renderedLine string, col int) string {
@@ -128,3 +138,44 @@ func (m *model) urlAt(line, col int) string {
 	}
 	return urlAtPosition(m.renderedLines[line], col)
 }
+
+// updateHoveredURL updates the hovered URL state based on mouse position.
+func (m *model) updateHoveredURL(line, col int) {
+	m.ensureAllItemsRendered()
+
+	if line >= 0 && line < len(m.renderedLines) {
+		plainLine := ansi.Strip(m.renderedLines[line])
+		for _, span := range findURLSpans(plainLine) {
+			if col >= span.startCol && col < span.endCol {
+				newHover := &hoveredURL{line: line, startCol: span.startCol, endCol: span.endCol}
+				if m.hoveredURL == nil || *m.hoveredURL != *newHover {
+					m.hoveredURL = newHover
+					m.renderDirty = true
+				}
+				return
+			}
+		}
+	}
+
+	if m.hoveredURL != nil {
+		m.hoveredURL = nil
+		m.renderDirty = true
+	}
+}
+
+// applyURLUnderline underlines the hovered URL in the visible lines.
+func (m *model) applyURLUnderline(lines []string, viewportStartLine int) []string {
+	if m.hoveredURL == nil {
+		return lines
+	}
+
+	viewIdx := m.hoveredURL.line - viewportStartLine
+	if viewIdx < 0 || viewIdx >= len(lines) {
+		return lines
+	}
+
+	result := make([]string, len(lines))
+	copy(result, lines)
+	result[viewIdx] = styleLineSegment(lines[viewIdx], m.hoveredURL.startCol, m.hoveredURL.endCol, underlineStyle)
+	return result
+}

pkg/tui/components/messages/urldetect_test.go

@@ -1,8 +1,10 @@
 package messages
 
 import (
+	"strings"
 	"testing"
 
+	"github.com/charmbracelet/x/ansi"
 	"gotest.tools/v3/assert"
 )
 
@@ -162,3 +164,51 @@ func TestBalanceParens(t *testing.T) {
 		})
 	}
 }
+
+func TestUnderlineLine(t *testing.T) {
+	tests := []struct {
+		name     string
+		line     string
+		startCol int
+		endCol   int
+		wantSub  string // substring that should appear underlined
+	}{
+		{
+			name:     "underlines URL portion",
+			line:     "visit https://example.com for more",
+			startCol: 6,
+			endCol:   25,
+			wantSub:  "https://example.com",
+		},
+		{
+			name:     "preserves text before and after",
+			line:     "before https://x.com after",
+			startCol: 7,
+			endCol:   19,
+			wantSub:  "https://x.com",
+		},
+		{
+			name:     "no-op when startCol >= endCol",
+			line:     "hello world",
+			startCol: 5,
+			endCol:   5,
+			wantSub:  "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := styleLineSegment(tt.line, tt.startCol, tt.endCol, underlineStyle)
+			if tt.wantSub != "" {
+				// The underlined text should contain the ANSI underline escape
+				assert.Assert(t, strings.Contains(result, "\x1b["), "expected ANSI escape in result: %q", result)
+				// The plain text of the result should still contain the URL
+				plain := ansi.Strip(result)
+				assert.Assert(t, strings.Contains(plain, tt.wantSub), "expected %q in plain text: %q", tt.wantSub, plain)
+			} else {
+				// No change expected
+				assert.Equal(t, tt.line, result)
+			}
+		})
+	}
+}

pkg/tui/tui.go

@@ -2447,7 +2447,7 @@ func getEditorDisplayNameFromEnv(visual, editorEnv string) string {
 func toFullscreenView(content, windowTitle string, working, leanMode bool) tea.View {
 	view := tea.NewView(content)
 	view.AltScreen = !leanMode
-	view.MouseMode = tea.MouseModeCellMotion
+	view.MouseMode = tea.MouseModeAllMotion
 	view.BackgroundColor = styles.Background
 	view.WindowTitle = windowTitle
 	if working {